Re: [PATCH 08/23] KVM: x86 emulator: cleanup some direct calls into kvm to use existing callbacks

[Gleb Natapov <gleb@redhat.com>]

On Wed, Apr 28, 2010 at 11:59:54AM +0300, Avi Kivity wrote:
> On 04/27/2010 03:15 PM, Gleb Natapov wrote:
> >Use callbacks from x86_emulate_ops to access segments instead of calling
> >into kvm directly.
> >
> >
> >
> >-static unsigned long seg_base(struct x86_emulate_ctxt *ctxt, int seg)
> >+static unsigned long seg_base(struct x86_emulate_ctxt *ctxt,
> >+			      struct x86_emulate_ops *ops, int seg)
> >  {
> >-	if (ctxt->mode == X86EMUL_MODE_PROT64&&  seg<  VCPU_SREG_FS)
> >-		return 0;
> >+	unsigned long base;
> >
> >-	return kvm_x86_ops->get_segment_base(ctxt->vcpu, seg);
> 
> get_segment_base() is only one vmread on intel, but you replace it
> with reading the entire segment.
> 
Didn't what to have separate x86_emulate_ops callback for reading
segment base. If this is serious performance concern it can be added

> >+	if (ctxt->mode == X86EMUL_MODE_PROT64) {
> >+		u64 val;
> >+		switch (seg) {
> >+		case VCPU_SREG_FS:
> >+			ops->get_msr(ctxt->vcpu, MSR_FS_BASE,&val);
> >+			break;
> >+		case VCPU_SREG_GS:
> >+			ops->get_msr(ctxt->vcpu, MSR_GS_BASE,&val);
> >+			break;
> >+		default:
> >+			val = 0;
> >+			break;
> >+		}
> 
> Why this ugliness?  get_cached_descriptor() should do this.
> 
get_cached_descriptor() returns struct desc_struct which is 32 bit only.
There is not 64bit segment descriptors.

> >
> >  static unsigned long seg_override_base(struct x86_emulate_ctxt *ctxt,
> >+				       struct x86_emulate_ops *ops,
> >  				       struct decode_cache *c)
> >  {
> >  	if (!c->has_seg_override)
> >  		return 0;
> >
> >-	return seg_base(ctxt, c->seg_override);
> >+	return seg_base(ctxt, ops, c->seg_override);
> >  }
> 
> Sticking ops into ctxt would reduce the size of these patches.
> 
But it will introduce intermediate huge patch. But I agree that this
should be done eventually. Planned to do it somewhere at the end. Near
the patch that change x86_emulate_ops callbacks to get ctxt instead of
vcpu as a parameter.

--
			Gleb.